Physical vapor deposition (PVD), also referred to as sputtering, uses a solid metal, such as titanium, as the source or target to deposit material on a substrate. During a PVD process, metal atoms are produced by dislodging them from the target with high energy ion bombardment. The high energy ions that cause sputtering are typically from a heavy inert gas, such as argon. The substrate is provided on a pedestal at a selected distance from the target and held at a negative potential with respect to the plasma generated by a power source. A major portion of the sputtered metal atoms or groups of atoms follow a substantially linear trajectory over a distribution of angles due to the low pressure maintained in the chamber. The gas composition and pressure in the sputtering chamber is typically achieved by evacuating the chamber down to about 10xe2x88x929 Torr before back-filling the chamber with argon to a pressure of a few millitorr. At these gas pressures, the pedestal can be raised upward within the chamber so that the distance between the target and the substrate can be less than the mean free path of the argon gas molecules. Therefore, many sputtered particles travel directly to the substrate without a collision.
However, a significant portion of the sputtered particles become scattered in the gas, due to collisions with the gas, electrical field effects and the like. These scattered particles can redeposit onto various surfaces of the chamber, e.g., onto the sidewall of the target itself. The material redeposited onto the sidewall of the target accumulates over time to form particles or sheets of the material. Direct current (DC) power is applied to the target during sputter deposition on a substrate and then removed from the target between substrates. Therefore, the target, as well as the redeposited material, is continually being heated and cooled, thereby subjecting itself to thermal stress. Over a period of time, this stress may cause particles of the material deposited on the target sidewall to come loose and fall onto the substrate. The material which adheres to the sidewall with low adhesion strength is more prone to come loose and degrade the particle performance of the chamber. The adhesion strength of the deposited material depends on the angle of incidence of the sputtered material as it collides into the sidewall. Generally, closer the angle of incidence is to the right angle, greater the collision force, and thus the greater the adhesion strength between the deposited material and the target sidewall.
The present invention provides a sputter target for a physical vapor deposition system that reduce particles generated during sputtering. According to one embodiment of the present invention, an apparatus for a physical vapor deposition system includes a target having a sidewall having an undercut thereon defining a net erosion area and a net redeposition area.
In another embodiment, a target for a physical vapor deposition system includes a lower surface, and a sidewall defined around the lower surface. The sidewall includes an undercut defining a net erosion area and a net redeposition area. Yet in another embodiment, a method for manufacturing a target includes determining a transition point on a sidewall of a first target. The transition point defining a net erosion area and a net redeposition area. An undercut is provided on a sidewall of a second target according to the transition point determined.